As is well known in the art, catheters are frequently used with electrodes on the surface thereof for selectively stimulating and/or sensing electrical activity in the body and particularly in connection with the heart. For example, a catheter may be inserted into the cardiovascular system of a patient, through the superior vena cava, and into the heart so as to achieve placement of one or more electrodes in desired positions within the heart or adjacent a portion of the heart to evoke a response of the heart muscle to an electrical signal applied to the electrodes. As the utilization of catheters in remote and difficult to reach portions of the body such as the heart has increased, it has become important to be able to precisely control the movement of the catheter.
Control of the movement of catheters is somewhat difficult because of the inherent structure of the same. The body of conventional catheters is normally long and tubular. To provide sufficient control over the movement of the catheter, it is necessary that its structure be somewhat rigid. However, the catheter must not be so rigid as to prevent navigation of the catheter through the body to arrive at the precise location where the medical procedure will be performed. In addition, it is imperative that the catheter not be so rigid as to cause damage to the portions of the body through which it is being passed.
Over the years, specific catheters have also been developed for very particular purposes. For example, temporary atrial defibrillation catheters have been designed which are used specifically for terminating atrial fibrillation of a patient in a hospital or other medical facility, whether spontaneous or induced by medical procedures being performed on the patient for analytical, pre-surgical, or other purpose, such as electrophysiology tests. The catheter is coupled to an electrical waveform generator to deliver electrical shocks to the patient's heart when activated by the attending physician or surgeon after implantation of the catheter. It is desirable that such a catheter be especially amenable to rapid insertion and manueverability into proper position to limit the period during which the heart is in atrial fibrillation.
As another example, mapping and ablation catheters use an electrode array on the catheter which allows for electrically mapping areas of tissue, in the heart or otherwise, and optionally ablating certain tissue areas where pathways that cause cardiac arrhythmias are identified using one or more of the electrodes. Radio frequency electrical current is then transmitted to the tissue via the catheter which is positioned as closely as possible to the arrhythmogenic site. The electric current heats the tissue surrounding the catheter and ablates the specified tissue.
These electrode catheters are usually formed by a continuous, electrically conductive coating or layer deposited or otherwise formed directly on the outer surface of the catheter at the distal end thereof. Preferably, this outer electrode may be formed by ion-beam assisted deposition using a preselected metal for efficient vaporization onto the designated surface region of the catheter body. Alternatively, the electrically conductive coating may be formed by sputtering the metal onto that region of the catheter or by vacuum deposition, spraying, or printing the electrically conductive material on the designated surface region. The result is an electrically conductive coating of desired thickness which provides a relatively uniform electrode throughout the desired length and surface region of the catheter body to improve the characteristics of electric field and an electrode which flexes to substantially the same extent as the catheter body without such a coating. That is, the electrode does not impede the flexibility of the catheter.
The electrically conductive coating is electrically connected to a conductive lead or leads running through a lumen of the catheter by means of a conductive material in one or more openings formed in the catheter wall from the outer surface of a catheter body to the interior surface of the lumen. These openings are then filled with an electrically conductive paste which firmly contacts both the conductive coating and an exposed conductive surface of the lead. The lead is, of course, electrically insulated from other leads associated with other electrodes which may also be employed on the catheter. A single connection and, therefore, a single opening is all that is required for interconnecting the surface electrode and the internal lead.
In order to ensure that at least that the electrode is sufficiently flexible so that the same can be easily bent and again straightened, as desired, without causing any damage to the same, it is formed by a process of ion-beam assisted deposition (IBAD). This technique is described in detail in each of U.S. Pat. Nos. 5,468,562; 5,474,797; and 5,492,763, the disclosures of which are incorporated herein by reference. The use of this technique for forming an electrode catheter is also described in co-pending U.S. application Ser. No. 08/751,436. Alternatively, that co-pending application, also describes applying the electrode by sputtering, vacuum deposition, printing, or spraying. Before commencing the deposition process, areas adjacent to the location in which the flexible electrode is to be formed are masked by chemical or mechanical masking techniques. As is known in the art, the masking is removed after the deposition process is completed.
The preferred metal used in the ion-beam assisted deposition process to form the electrode is silver. However, other biocompatible low resistance metals such as gold or platinum could be utilized. The silver is vaporized and applied in a vacuum in a pure uniform coating of approximately 1 micron or less. However, the electrode could range in thickness from about 0.5 to 10 microns.
The problem with these methods however, is in the masking step, both in placing it on the catheter and removing it from the catheter once the deposition process is completed. Placing the masking on the catheter is time-consuming and may lead to inaccuracies. These catheters can be extremely small and to manually mask them is extremely tedious and may be difficult in some cases. Also, with this method, only 360.degree. sections of the catheter can be easily masked. If a section less than 360.degree. needs to be electrically conductive, trying to mask such an area may not only be difficult, it may lead to inaccuracies. Furthermore, removing the masking may be also be difficult, depending on the size of the catheter. Finally, the masking may not be completely removed, causing the residue to interfere with the functioning of the electrode.